{"id":"CVE-2026-27469","aliases":["GHSA-9fww-8cpr-q66r","PYSEC-2026-2527"],"title":"Isso affected by Stored XSS via comment website field","summary":"Isso affected by Stored XSS via comment website field","severity":"medium","cvss":6.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","vendor":"isso","product":"isso","ecosystem":"pip","affected":["isso < 0.13.2"],"patched":["isso 0.13.2"],"published":"2026-02-24","updated":"2026-07-13","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-9fww-8cpr-q66r","references":[{"url":"https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27469"},{"url":"https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"},{"url":"https://docs.python.org/3/library/html.html#html.escape"},{"url":"https://github.com/isso-comments/isso"}],"tags":["osv","pip"],"epss":0.00224,"epssPercentile":0.13279,"ingestedAt":"2026-07-13T18:57:55.932Z","slug":"CVE-2026-27469","body":"## Overview\n\n## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/<id>) and the moderation edit endpoint (POST /id/<id>/edit/<key>).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/<id>, POST /id/<id>/edit/<key>), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape — note the quote parameter\n\n## Affected packages\n\n- `isso < 0.13.2`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `isso 0.13.2`","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":33.6,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}